Graf hails 'incredible' Serena

Steffi Graf hailed Serena Williams for an "incredible performance" in matching her long-standing Open Era record of 22 Grand Slam wins.Williams won her seventh Wimbledon title with a 7-5, 6-3 win over Graf's German compatriot Angelique Kerber at the All England Club on Saturday."What an incredible performance by Serena at Wimbledon," Graf wrote on her Facebook page."Such a gift to all sport fans who get to continue to watch her add to an already amazing career #22!!! "Also, well done to Angelique making Germany so proud with her talent and fighting spirit!"Men's world number one Novak Djokovic, who saw his title defence end in a shock third-round defeat to Sam Querrey, also tweeted his congratulations.The Serb concentrated on the number 22 rather than the American's age of 34.